Electrostatic dot matrix printing techniques developed through the prior art generally comprise three basic steps. First, electrostatic charges are placed on the surface of a high resistivity paper having a thermoplastic coating by applying voltage pulses to electrodes of desired configuration positioned near the paper, the pulses having magnitudes in the order of 1,000 volts and durations in the microsecond range. Second, the electrostatic charges which form a latent electrostatic image on the high resistivity paper are made visible by passing the paper through a bath of dry inking powder which adheres to the charged area. Third, the ink powder is permanently bonded to the copy by heating the thermoplastic coating on the paper to its softening point and having the ink lightly pressed into it.
Although much progress has been made in the inking and permanent bonding steps, many problems yet remain in the initial charge forming process. The dot matrix type electrostatic printer of the prior art generally requires at least one transistor or other solid state driver device operating in or near the 1,000 volt range for the generation of each dot in the matrix. This requirement for a large number of drivers operating under high potential stress has resulted in a costly printer having poor reliability and has contributed to limiting the commercial success and applicability of the electrostatic printer.
It is known in the display panel art that ion discharge paths may be sustained and deviated or transferred at lower voltage potentials than those required to initiate the ionization paths in the first place. Effective use of this transfer phenomenon to reduce driver constraints have been made in the display panel field as disclosed in U.S. Pat. Nos. 3,617,796, 3,648,093, 3,673,461, 3,699,376, and 3,846,669, all assigned to the assignee of the present invention. Further use of the ionization transfer phenomenon in the panel display field is described in the article "Dot Matrix Display Features Inherent Scanning Ability", ELECTRONICS, March 1970, pp. 120-125. However, within the knowledge of applicant, the ionization transfer phenomenon has not yet been effectively harnessed for use in an electrostatic printer.